Method for making high-speed-steel tool castings



Jan. 7, 1930. A. c. DAVIDSON METHOD FOR MAKINGHIGH SPEED STEEL TOOL CASTINGS Original Filed Dec. 27,1924 2 Sheets-Sheet 1 INVENTQR Arflwr a 111m ATTORNEY Jan. 7, 1930- A. c. DAVIDSON 1,742,849

METHOD FDR MAKING HIGH SPEED STEEL TOOL CASTINGS Original Filed Dec. 27, 1924 2 Sheets-Sheet 2 INVENTOR Arflmr c Davida; 5% I ATTORNEY Patented Jan. 7, 1930 UNITED STATES PATENT OFFICE l ARTHUR C. DAVIDSON, OF COLLINSVILLE, CONNECTICUT, ASSIGNOR TO DYCAST STEEL COMPANY, A COPARTNERSHIP COMPOSED 01 A. C. DAVIDSON AND H. W. HENKE,

OF COLLINSVILLE, CONNECTICUT METHOD FOR MAKING HIGHSPEED-STEEII TOOL CASTINGS Application filed December 27, 1924, Serial No. 758,858. Renewed May 28, 1929.

This invention relates to the production of high speed steel tool castings such for example as dies, punches, rivet sets, disc blanks and the like, and has for its object to lower production cost and improve the uality of the castings at the same time. eretofore high speed steel tools have been cast singly in sand molds where the expense of makinga large number of molds is great by reason of 1 the cost of the fine quality of sand requiredand the cost in time and labor of tamping the sand in the flasks to uniform density. For cored castings the production of a large number of sand cores becomes likewise expensive.

The losses in head and gate sections where.

the tools are cast singly is substantial. According to this invention a plurality of high speed steel tool castings are formed simultaneously, superposed axially in a mold preferably of cast iron. The metal is poured below the top of the mold cavities and flows upwardly, and then additional metal is poured in on top to a depth sufficient to fill and prevent formation of any shrinkage caviing. While this process is not limited to any particular steel yet very good results are ob tainable with a pure steel which does not form segregations whereby elimination of 1 any tendency to form cavities or weaknesses due to the steel and to the cooling in mold are both overcome. y

In the accompanying drawings:

Figure 1 shows one half of an embodiment of this invention with the castings in place and the other half mold removed,

Fig. 2 is a top view of the device shown in 50 Fig. 1,

ties within the castings. The supply or flow- Fig. 3 illustrates another embodiment of the invention,

Fig. 4 is a top view of the device of Fig. 3,

alining the two halves of the mold when clam ed together for the pouring operation. In Flg. 1 is shown a number of similar castings 12 arranged end to end to form an elongated casting. The pouring gate 13 has an enlarged mouth 14 and is curvedat 15 just before entering the mold for the purpose of reducing splatter and having the metal flow in a substantially continuous stream as it rises in the mold from the bottom .16 to the top of p the mold. The castings 12 are punching dies for use in heavy presses. The metal mold is provided with a number of chokes 17 to mark the separation between the dies. These chokes are of sufiicient width so that the several castings may be separated by sawing them apart without the trouble of laying out the line of cut and without danger of cutting too much into the allowable dimensions of any casting. The castings adjacent the pouring gate do not abut as closely as the rest of the castings but are separated by a section between the chokes 18,- which,.because of its being opposite the pouring gate may be under greater likelihood of having shrinkage or suction feed cavities formed therein to weaken the metal. To'avoid the necessity of discarding one or two castings by reason of any internal weaknesses of this sort the block of metal between the chokes 18 is discarded as waste along with the sprue section and head. A small overflow passageway 19 is arranged preferably above the castings 12 so that as the metal is being poured and rises upwardly its height may be determined when it reaches the overflow passage 19. Also any impurities which may be floating on the metal are withdrawn through this overflow passage. A block 20 of wood or of refract ry material is then inserted in the passa eway 19 before the head 21 is poured. Ad acent the mold cavity the pouring gate 15 is provided with a choke 22 of about the same size as the other chokes 17 and 18 and so arranged as to cause this restricted portion of the gate to freeze quickly after pouring ceases and before the head 21 is poured. Contiguous tools are preferably arranged with their large ends together to facilitate axial flow of hot metal and lessen coolin effect of mold.

-In Figs. 3 an 4 the two-part mold 23 is also of metal. The castin s 24 shown in Fig. 5 are intended to be finis ed into threading dies. The core 25 is of sand and the bottom portion of the mold is tapered, as illustrated at 26, to accurately center the core. A bridging piece 27 engages the upper portion of the core and holds it in position. Chokes 28 indicate where the castings may be sawed in separating and a similar choke 29 is located within the gate for the same purpose of causing the gate to freeze as soon as pouring ceases. The mold of Figs. 3 and 4 is also provided with an overflow passageway 30 on block 31. As illustrated in Fig. 3, the gate adjacent the mold is rounded so as to allow the incoming stream of metal to flow downward into the bottom of the mold more accurately than it would flow over a sharper ed e.

11 Figs. 6 and 7 is illustrated another embodiment in which the pouring gate has a still more gradual slope ad'acent its entrance to the mold to facilitate t e pouring of the molten stream without splatter. The mold is provided with projections 33 which form recesses within the castings and lessen the amount of machining necessary in finishing these castings 35 into heading dies, for example. A similar overflow passageway 34 is provided and the chokes 36 indicate the limits of the castings and where to saw in separatin them.

in operation, with castings for the pur-' poses illustrated a high grade of tool steel is desirable. With iron molds, because the outer surfaces of the casting are chilled or cooled quicker, there is a greater tendency for shrinks, piping and similar weaknesses to form due to the cooling metal sucking a more fluid material from'the center in cooling and shrinking. With the molds arranged as illustrated, it is ossible to make the castings substantially e'e from these shrinkage cavities by locating the first pouring gate below the top of the mold cavity, or preferably intermediate its ends, as illustrated, filling the mold below the gate and then filling that portion above by continuing the pouring operation and flowing hot metal through the center or axis of the eastin between the cooling walls where it is nee ed to prevent the formation of shrinkage cavities. In pouring,

metal is poured in through the first gate until above the castings and until it overflows through the passageway indicated. Pouring throughthe first gate is then suspended when the choke within this gate enables it to freeze rapidly. Additional metal of the same kind is then poured into the mold from above through theupper opening or gate to form the head indicated at 21 in Fig. 1. When the pouring gate freezes there is then no likelihood 0 the head flowing through the casting and up through the first gate to overflow the gate and weaken the castings. Supplying hot metal to form the head 21 has been found to give better results and better quality castings than would be made if the head 21 were the molten metal poured in to form' this may be discarded and the shrinkage caviv ties do not extend to any of the castings. Upon removal from the mold, the sand core, if one is used, can be taken out and then the metal sawed off to make the desired separate tools. If necessary the elongated castings are subjected to a heat treatment for softenin them before sawing. The hot metal supplied or flowing between cooling outer portions of the casting fills u.%any transverse or longitudinal shrinkage c vities which may tend to form by the chilling act-ion of the metal mold and the natural shrinkage of the metal in cooling, and prevents then formation in the finished tool casting. Pouring themetal in metal axially and tends to fill up any shrinkage cavities which may form in the lower half of the mold below the gate, while the supply or flowing of the hot metal upwardly through the axis of the castings fills any such cavitles which may tend I to form in any castings above the gate. The hot metal poured for the head causes all piping to form in the head and not in the tools. It has been found that smoking the metal mold produces beneficial results in preventing molecular union between the mold and casting and in preventing any splashes from sticking to the walls of the mold although in this invention precautions are taken to avoid splashing the metal as described. While this process and apparatus are not limited to any special kind of a metal or steel tool yet it is especially adapted for steels having a high degree of purity where the tendency to segregations is reduced and a uniform texture of metal obtained without the use of this particular casting process and mold. But this casting process cooperates with a steel having a high degree of purity, which does not tend to form segregations, and results in the production of still etter quality high speed steel tool castings than has heretofore been possible.

Such a process for preparing a-high speed steel tool casting comprises making up the -melt of such materials as iron, tungsten and chromium 1n any desired manner to secure molybdenum, uranium, etc., which wouldotherwise be volatilized or oxidized and lost, can now be added. The vanadium used at this time is for scavenging, and not for alloying, as alloying vanadium is added later so as not to be oxidized.

, After the last mentioned alloys such as cobalt, etc. are added, oxidation of the alloys is prevented by another treatment with the same mixture, while holding at or above 3400 F. during 30 minutes or more. The temperature is now dropped to about 3200 F. and a charge similar to that before used is employed except that it is somewhat less than one-half as much, and contains some iron scale. Tantalum amounting .to .1% of the melt is preferably added to this charge. These charges are in packages tied to iron rods so as to be inserted by the melter at the bottom of the electric furnace or crucible. The melt immediately becomes more fihid and quiets down as the heat is raised to above 3200 F. to about 3400" F. and maintained for 10 minutes. Alloying vanadium can now be added with only an allowance for loss of 20% to 30% as compared with over for previous practice,- while maintaining say 3300 F. for about 10 minutes.

The bath is not yet free from impurities and is subjected to a violent almost explosiveaction which acts mechanically as well as chemically to expel the residue of oxides, occluded gases, slag, fragments of brick from the furnace lining, sulphur and phosphorus. The treatment at this time also has the function of increasing the fluidity of the bath and must not introduce objectionable matters therein. After holding the temperature at about 3300 F. to 3500 F. a mixture of alloys, silicon, manganese, aluminum, titanium and magnesium, together with a small percentage of iron oxide, amounting to about 52% of the charge is added. This mixture is composed partly of lumps and partly of finely powdered alloys according to the necessity and analysis. The action of this mixture of lumps and powder is for the powder to go off first with a comparatively violent reaction and then for a-larger reaction to occur due to the mass of the lumps, the whole resulting in what is practically an explosion at the bottom of the pot or furnace, which not only violently disturbs the bath causing occluded gases to pass out but also carries away any solld impurities and thoroughly mixes the entire bath. After the explosion there is substantial freedom from sulphur, phosphorus, oxides, gases, slag and other impurities andalso a complete amalgamation into ahomogeneous alloy. v

In the specific explosive mixture powdered magnesium may be used for both its mechanical and chemical effect, and other agents for chemically producing a mechanical agitation of the bath may be used such as a small percentage of gunpowder. Due to the cxotherinic action of the explosive scavenging treat ment the temperature may rise as high as 3600 F. without any damage to the metal. The metal is now poured into the molds illustrated in the drawings according to the process previously described.

Among the advantages of this invention is the saving in losses from making a number of castings simultaneously. If one casting be made at a time, substantially as large a head is necessary to prevent piping extending within the casting, and almost as large a sprue section or pouring gate is necessary, so that by pouring a number of castings together the losses are greatly reduced. For example if five castings are made at once, as illustrated in Fig. 6, the losses are almost,

if not substantially one-fifth of What they Would be were one casting made at a time. Another advantage of this invention resides in the production of castings free from shrinkage cavities, piping, blow-holes, and the like, which Weaken the casting and prevent its being used where large stresses are met with. The use of iron molds for casting tool steels is usually attendant with the formation of shrinkage cavities by reason of the rapid cooling or chilling due to the surfaces of the mold, but under this invention where highly fluid metal is supplied to the axis of a plurality of-castings, the use of a metal mold is made possible for high speed steel tools cast to form without shrinkage or suction feed cavities forming. Another advantage of the metal molds is the ability to use them over and over again without the labor cost of building up a sand mold, and then again the outer surface of the form castings is smoother and requires less finishing, so that the castings from metal mold may be made more nearly to the required size. So far as known the advantage of metal molds has never before been available for use in casting high speed steel tools owing to the rapid cooling which formed objectionable shrinkage cavities. Under .this invention, losses are reduced and the advantages of a metal mold are made possible for use with good quality tool steel for making castings adapted to withstand heavy stresses without danger of having the shrinkage cavities formed within them. The arrangement of tools as illustrated in Fig. 1 with their larger ends contiguous lessens the number of reduced ortions and the cooling effect of the mold since a casting having a greater number of reduced portions cools more rapidly than one having fewer such portions. Also lessening the cooling effect of the mold facilitates flow of hot metal between cooling walls of the casting to fill any shrinkage cavities. A further advantage resulting from the arrangement of tools with their similar ends contiguous is the saving in number of cores necessasry in event that only the one end of each is cored. Thus in Figs. 6 and 7 a projection 33 serves for two tools when similar ends are together.

While this invention is not limited to any particular type of steel, yet examples of a very hard and high grade steel may include the following composition: tungsten 14%, chromium 4%, vanadium 1%, carbon .4%, balance iron; or some cheaper grade of steel may be used, such as one having from .1 to .75% carbon, .1 to .8%- manganese, .05 to .8070 silicon, a maximum of not over .045% sulphur and phosphorus, and the balance iron. Another advantage is the manner in which the sand core is accurately centered and retained in position at both the top and bottom, the tapered recess in the bottom of the mold being filled in with sand around the core to prevent metal being poured in. The combination of a casting process which overcomes the tendency for shrinkage cavities to form, with a high speed steel which is of relatively great purity and which does not tend to form segregations but a uniform structure, together result in the production of a higher grade high speed steel tool cast to form than has ever heretofore been possible.

I claim: 7

l. A method of manufacturing a plurality of high speed steel tools in one operation whichconsists in arrangin aplurality of mold cavities vertically an axially aligned with the center of each cavity opening directly into the center of the adjacent cavities and then pouring the metal upwardly through the center of the series of cavities.

2. A method of manufacturing a plurality of high speed steel tools in one operation which consists in arrangin a plurality of mold cavities vertically an axially aligned with the center'of each cavity opening directly into the center of the adjacent cavities and then pouring the metal upwardly through the center of at least some of the cavities.

3. A method of manufacturing a plurality of high speed steel tools in one operation which consists in arranging'a plurality of mold cavities vertically and axially aligned with the center of each cavity opening directlyinto the center of the adjacent cavities and then pouring the metal upwardly through the center of the series of cavities to above the uppermost cavity, then pouring a head on top of the metal first poured, said head being of sufficient depth to have all the piping and shrinkage cavities occur in the head alone.

4. A method of manufacturing a plurality of high speed steel tools in one operation which consists in arranging a plurality of mold cavities vertically and axially aligned with the center of each cavity opening directly into the center of the adjacent cavities and then pouring the metal upwardly through the center of the series of cavities to above the uppermost cavity then pouring a head on top of the metal ti being of sufiicient depth to have all the pip.- ing and shrinkage cavities occur in the head alone and drawing off a little metal from the topdof that first poured before pouring the hea 5. A method of manufacturing a plurality of high speed steel tools in one operation,

rst poured, said head each having one end larger than the other which consists in arranging a series of mold cavities vertically and axially aligned with the enlarged ends of contiguous cavities placed together and with the center of each cavity opening directly into the center of the adjacent cavities'and then pouring the metal upwardly through the center of the series of cavities.

Signed at Collinsville in the county of Hartford and State of Connecticut this 22nd day of December A. D. 1924.

. ARTHUR C. DAVIDSON. 

